To Carry Out Tolerance Analysis of an Aeronautical Assembly Involving Free Form Surfaces in Composite Material

The present work deals with the tolerance analysis of freeform surfaces belonging to parts in composite material and that may be non-rigid. The aim of this chapter is to present the steps to carry out the tolerance analysis of an assembly involving free-form surfaces in composite material by using a commercial CAT software. The great effort of the present work is overcome the limits of the CAT software to deal with dimensional and geometric tolerances applied to free form surfaces in composite material. This paper tries to answer to some questions on tolerance analysis without clear answer: What are the functions of the product, how do we flow down these key product functions through into its detail parts? How to model a free-form surface for a tolerance analysis? How to deal with a composite material for a tolerance analysis? How to improve the assembly process in order to reduce the tolerance impacts on these functions? An aeronautic component is considered as case study. This is an internal frame of a winch arm mounted on an helicopter. The part addressed in this paper is the after internal frame that allows to mount the fairing covers of the head of the winch arm directly on its structural beam. It is made in carbon fiber composite material. The frame is made with five layer of carbon fiber imbued in a matrix of epoxy resin for a total stack thickness of 1.65 mm. After the stratification process, a curing process is carried out by autoclave with a control of temperature and pressure. The weight of the part is about 350 g. Assembly operation among the parts are done by using special grub screws that are inserted in the holes of each component. No adhesives or resins are used to secure the surfaces, since a perfect adhesion is not required.